The present invention relates to an improved high-pressure pump.
It applies in particular to a high-pressure pump for supplying a motor vehicle internal combustion engine with fuel. In this case, the transferred liquid is fuel.
The state of the art already knows a high-pressure pump for pumping a first liquid, known as the transferred liquid, of the type comprising a main unit for pumping the transferred liquid, which unit is actuated by a secondary unit for pumping a second liquid, known as the working liquid, the secondary unit comprising at least one piston for compressing the working liquid, equipped with an axial drilling for circulating working liquid between a reservoir and a working-liquid compression chamber, this compression chamber being delimited by a flexible diaphragm for pumping transferred liquid, this diaphragm being arranged in the main unit.
A pump of this type is described for example in WO 97/47883.
The piston for compressing working liquid described in that document comprises a swiveling head in which an emerging end of the axial drilling is formed. This swiveling head rests against an inclined face of the swashplate via a sliding pad which is pierced so as to allow the working liquid through. A cavity formed in the inclined face of the swashplate makes it possible, according to the relative position of this cavity and of the shoe, to alternate, as the swashplate rotates, the placing of the axial drilling of the piston in communication with the reservoir and the isolating of this axial drilling from this reservoir.
For the pump to operate satisfactorily, the cavity formed in the swashplate needs to be precisely dimensioned. If this precision is not achieved, undesirable pressure fluctuation is observed in the main and secondary pumping units. Now, the precision required is not always compatible with the manufacturing tolerances and dimensional spreads generally admitted in the conditions of mass-production of the pump.
Furthermore, recourse to sliding shoes poses problems of dynamic sealing.
Finally, the diaphragm delimiting the compression chamber is usually elastically returned by a spring to a position that tends to reduce the volume of this compression chamber. For the abovementioned reasons of pump operating effectiveness, the diaphragm return spring needs to be dimensioned precisely, and this is not really compatible with mass-production of the pump.
It is an object of the invention to propose a high-pressure pump of the aforementioned type which is simple to manufacture and very reliable.
To this end, the subject of the invention is a high-pressure pump of the aforementioned type, characterized in that the piston comprises a valve for shutting off the axial drilling and housed in this drilling between two ends of this drilling in permanent communication with the reservoir and the compression chamber respectively, the valve opening as soon as the pressure of the working liquid in the reservoir exceeds that of the working liquid in the compression chamber and closing if the reverse is true.
According to other features of the invention:
the drilling is stepped and comprises a large-diameter portion opening into the compression chamber and a small-diameter portion opening into the reservoir, the valve comprising a ball housed in the large-diameter portion so as to be able to be moved between, on the one hand, a shoulder separating the large-diameter and small-diameter portions, forming a seat onto which the valve closes and, on the other hand, a stop that limits the opening travel of the valve;
the compression chamber is formed in a body of the secondary unit, in which body the piston is slidably mounted, this piston comprising an end external to the body returned elastically into contact with a thrust rolling bearing carried by a swashplate for actuating the piston;
the diaphragm separates the compression chamber from a variable-volume pumping chamber for the transferred liquid, the diaphragm being moveable between a first position in which the pumping chamber has maximum volume, toward which position this diaphragm is elastically returned by a spring known as the diaphragm spring, and a second position in which the pumping chamber has minimum volume, the stiffness of the diaphragm spring being chosen so that this diaphragm spring keeps the working liquid contained in the compression chamber at a raised pressure with respect to the working liquid contained in the reservoir for as long as the diaphragm has not reached its first position; and
the transferred liquid is a fuel for a motor vehicle internal combustion engine.